captions are on! to turn off, click cc at bottom right. follow us on twitter (@amoebasisters) or facebook! chances are in your life, you’ve had thecommon cold before. the cold is extremely common. you know, it causes the sneezing andthe coughing and just makes you feel awful. the worst thing about the cold is that youcan take medications to help with the symptoms, but you really can’t treat the actual cold.you can’t really get rid of what causes it. why is that? the reason for this is because most coldsare caused by viruses. we’ve talked before about antibiotics; they only work on bacteria.viruses are definitely not bacteria. so antibiotics
have no effect on viruses. in fact, virusesaren’t even cells at all. you can’t say that viruses are a prokaryote or a eukaryote.it’s not a cell. it doesn’t have a cell membrane like all cells have; it doesn’thave a lot of cell components. it’s a non-living structure. in fact, viruses can’t even reproduceon their own. so, viruses aren’t even alive, which makes them very difficult to treat.let’s talk about what they actually have. what is their structure? one thing all viruses have in common is thatthey have some type of genetic material. this does not mean they can reproduce on theirown, but they are going to use their genetic material and force their host to reproducethemselves. this genetic material, for some viruses, is in the form
of dna. for other viruses, it’s rna. virusesalso usually have some kind protein coat, also known as a capsid. capsid is a vocab wordto think of that can protect that dna or rna genetic material. another thing to mentionis that viruses are very, very small; they are much smaller than bacteria. you typicallyare going to need an electron microscope in order to see a virus. it’s very, very small. viruses can also contain other structures.some of them package special enzymes with them. some viruses have an outer envelope.there are different varieties of what viruses can have, but they main thing is that theyhave genetic material and they typically have some kind of protein coat, also known as acapsid. now, viruses are very, very specific.
so you’ll want to think of them as picky.usually, viruses have specific types of cells that they go after. so let’s talk about viral reproduction,because we did mention that they can’t reproduce on their own and their very, very specificfor the host that they’re going to go infect. so the first cycle of the two we’re goingto talk about is the lytic cycle. in the lytic cycle, the virus (remember they're very selective)attaches to a host cell, and it’s going to inject either its dna or rna, dependingon what kind of genetic material it has, into the cell. you would think the cell would noticethis, but in many cases it does not. it takes that genetic material and it starts followingthe instructions, which in this case is very
bad. in this case it makes copies of the virus.it starts making so many copies of the virus that usually it’s going to cause the cellmembrane of the host to rupture, explode, lyse! so what happens is now these new viralcopies get out of the cell, and they go and infect other cells. this is very bad. thisis known as the lytic cycle. by the way, the lysing of the cell membraneis a very bad thing for the cell. the cell cannot survive without its cell membrane.it’s definitely not a good thing for a cell. the other cycle is called the lysogenic cycle,and i like to remember this is the longer word so i like to think of this as the longer,sneaky cycle. a lot of times when we’re talking about this cycle, we’re talkingabout a special kind of virus called a bacteriophage.
it sounds very fancy, but what it means isthat it is a virus that goes after bacteria. in many cases, when we’re talking abouta lysogenic virus, this is what we’re talking about. these types of viruses that go throughthis cycle, they do kind of the same thing at the beginning. they inject their geneticmaterial, but this time, the genetic material stays hidden in the host dna. what happensis that when the host replicates it also replicates the viral dna. eventually, what can happenis that it can be triggered to go into the lytic cycle and then the virus can start beingassembled and lyse out of the cell. in the meantime, whenever it’s during the lysogeniccycle, it’s kind of hidden in there. it’s kind of a sneaky kind of thing. as far aswhat triggers as what triggers it to go into
the lytic cycle, it can be a variety of things.scientists are still doing a lot of studies about this. sometimes we notice they are environmentaltriggers like uv radiation or chemical triggers, but it can cause the virus to suddenly switchinto the lytic cycle. so going back to the cold, which again istypically caused by a virus, a lot of times it has to run its course. your immune systemwill take care of it. some viruses are extremely complicated, like hiv, a virus that can lead to aids. the host that it goes after are immune cells. by going afterimmune cells, it makes you very vulnerable to other infections. in fact, for someone who has hiv, the common cold could be very detrimental to their health. it’s something thatscientists are really researching to try to
treat. it’s difficult, too, because hivis a virus that tends to mutate quickly and so if the medications are very selective againstone specific type of virus and the virus mutates, it makes it difficult to treat. so with our talk today about viruses, youmight wonder, “is there anything positive about viruses?†well, viruses do play amajor role right now in gene therapy. it’s a very big field right now that is growingwith research. viruses do play a big role with that. also, scientists are looking forways to manipulate or engineer viruses; for example, there is a type of virus that goesafter insects. it’s called the nuclear polyhedrosis virus. i highly encourage you to look it up.this virus is very selective; it goes after
certain insects. however, if it could be targetedto a certain type of insects, the types that eat your crops, then it could be a great formof a pesticide. the only problem is that whenever you add some kind of pesticide, whether chemicalor viral, there can be major consequences in the ecosystem. when we get to ecology,we will talk about that. viruses are a major component of scientific research right now.that’s it for the amoeba sisters, and we remind you to stay curious.
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